How to Build a Raised Garden Bed: A Weekend Project Anyone Can Do

If gardening projects were ranked by payoff per hour of effort, the raised bed would win by a street. One afternoon of extremely forgiving carpentry — four walls and some screws, no joinery, no talent required — buys you years of better drainage, warmer spring soil, defined edges the lawn cannot invade, perfect soil you chose yourself, and a garden you tend without kneeling in mud.

This is the complete plan: dimensions that decades of gardeners have converged on, an honest materials comparison, the tool and cut list for a standard bed, assembly step by step, the rodent question, and — the part that surprises everyone — how to fill the thing without buying a small truckload of bagged soil.

Why Raised Beds Earn Their Reputation

• Perfect soil on day one, whatever disaster lies beneath — clay, rubble, sand, or compacted lawn.
• Drainage by design: beds shed excess rain instead of puddling, and never get walked on, so the soil stays loose for roots.
• An earlier spring: raised soil warms faster, buying you one to several weeks at each end of the season.
• Fewer invaders: lawn grass stops at the wall, slugs face a climb, and a mesh floor stops burrowers cold.
• Your back’s favorite garden: even 30 cm of height transforms weeding; 45–60 cm nearly eliminates bending.

Dimensions: The Numbers That Matter

Width — the one hard rule

Maximum 120 cm if reachable from both sides; maximum 60–75 cm against a wall or fence. The entire logic of a raised bed collapses the day you step into it and compact the soil, so every centimetre must be reachable from the edges. When in doubt, narrower.

Height — pick by purpose

Length — whatever suits, in reason

200–250 cm is the sweet spot: standard lumber lengths cut without waste, and the sides stay stiff. Longer beds work but want a mid-span stake on each long wall to stop soil pressure bowing the boards. Leave at least 45–60 cm of path between multiple beds — wheelbarrow width if one exists in your life.

Materials, Compared Honestly

Avoid entirely: old railway sleepers and any vintage wood oozing tar (creosote), and reclaimed wood of unknown treatment history. Free boards are only free when you know what is in them.

Siting: Where the Bed Should Live

The frame is movable in theory and never in practice — soil makes decisions permanent, so choose the spot like it is forever:

• Sun first: 6+ hours of direct light for vegetables, measured, not assumed. Watch the candidate spot across one full day, remembering nearby trees cast longer shade in spring and autumn than in July.
• Water within hose reach. A bed twenty metres from the tap gets watered heroically in May and wishfully in August.
• Level-ish ground: minor slopes are absorbed by digging the high-side posts in deeper; real slopes want the bed run along the contour, or a terraced pair.
• Orientation: on open ground, a long axis running roughly north–south gives both long sides equal sun. It is a nicety, not a law — sun hours outrank compass points.
• Not over utilities or against wood you care about: know what is beneath before spiking posts, and leave an air gap between the bed and any fence or siding that would rather not spend a decade damp.

The Build: A 200 × 100 × 30 cm Standard Bed

Shopping and cut list

• 2 side boards: 200 cm × 30 cm (or two stacked 15 cm boards per side), ~4–5 cm thick
• 2 end boards: 100 cm × 30 cm (same stacking option)
• 4 corner posts: 7×7 cm (or so) × 45 cm — 30 cm inside the bed, 15 cm spiked into the ground
• Exterior-grade screws, 70–80 mm (about 24–32)
• Optional: galvanized hardware cloth / fine wire mesh for the base, plus staples
• Optional: 2 mid-span stakes for beds over 250 cm

Tools

Cordless drill with driver bits, saw (or have the store cut to length — most will), tape measure, spirit level, carpenter’s square or any rectangle you trust, mallet, pencil. Nothing exotic.

Assembly, step by step

1. Prepare the site: choose 6+ hours of sun, roughly level ground. Mow, then lay overlapping plain cardboard over the footprint and beyond it by 10 cm — the no-dig grass smotherer.
2. Build the frame upside down on any flat surface: screw each corner post flush to the top edge of the frame-as-inverted (which becomes the bottom when flipped, leaving the post spikes projecting). Attach both end boards to their posts first — three screws per joint, pilot-drilled near board ends so nothing splits.
3. Add the long sides, screwing into the same posts. You now have a rectangle with four legs in the air.
4. Check square: measure both diagonals; nudge the frame until the two numbers match. Square now saves crooked forever.
5. Rodent-proof if needed: with the frame still inverted, staple hardware cloth across the entire base, edges turned up along the inner walls. Skip plastic sheeting always — a bed needs to drain and let worms commute.
6. Flip and place: stand it on the cardboard, spikes down, and persuade the posts into the ground with the mallet until the frame sits flat. Check level along the top — a bubble’s worth of slope is fine; a visible tilt sheds water to one end all season.
7. Optional finishers: a flat capping board around the rim makes a seat and a mug shelf; raw linseed oil on outer faces adds a season or two of life to budget lumber.

Filling It Without Buying a Soil Mountain

A 200×100×30 bed swallows some 600 litres. Filling entirely with bagged mix is the expensive way; the layered fill (a mild version of hügelkultur) is how experienced gardeners do it:

1. Bottom third — coarse organic matter: branch trimmings, twigs, coarse wood chips, dry leaves, plain cardboard tubes. This bulk rots slowly into nutrition and sponge, and costs nothing.
2. Middle — rougher compostables: half-finished compost, grass clippings, straw, more leaves, tamped down.
3. Top 15–20 cm — the growing layer: roughly 50–60% quality topsoil, 30–40% compost, ~10% something airy (perlite, coarse sand, or leaf mold), mixed. This is the only layer roots meet in year one, and the only layer worth spending on.

Water the whole lasagna thoroughly, let it settle a few days (it will drop several centimetres — normal), top up, and plant. Each following spring the bed asks only for a 3–5 cm compost top-up as the lower layers digest and sink.

The First Planting and the First Season

• Plant densely — raised-bed spacing runs tighter than seed-packet rows, because you never need walking gaps inside the bed. Blocks, not rows.
• Mulch the surface once seedlings are up; raised soil drains beautifully, which also means it dries faster than ground level. Expect to water somewhat more often, deeply as ever.
• Tall crops (climbing beans, tomatoes) go on the bed’s north side so they shade the path, not the lettuce.
• Keep a foot out of it. Forever. That is the whole maintenance contract, along with the annual compost centimetres.

Variations on the Standard Bed

• The wall bed (60–75 cm wide): same build, one long side against a fence — remember reach comes from one direction only, so resist the wide temptation.
• The L or U layout: two or three standard beds meeting at corners wrap a working area in growing space; keep every interior path at that 45–60 cm minimum, and cap the rims for a continuous seat.
• The tiered bed: two frames of different heights stepped against each other — herbs and strawberries spilling from the upper tier, roots luxuriating in the deep lower one. Same corner-post construction, one shared wall.
• The accessible bed (60–75 cm tall, max 60 cm reach): built for gardening from a chair or without bending; go generous on corner posts and mid-span stakes, since soil pressure scales with height, and lean hard on the layered fill to keep costs sane.
• The kids’ bed: a half-size frame (100 × 60 × 20 cm) with its own trowel and full sovereignty. Radishes, sunflowers, and cherry tomatoes have recruited more lifelong gardeners than any lecture.

Upgrades Worth Bolting On

• Drip irrigation: a raised bed is the perfect drip candidate — one line looped through the bed on a tap timer, mulch over the top, and summer watering becomes a checkbox. Install it while the bed is empty if you know it is coming.
• Hoops and covers: three arcs of flexible pipe slipped over rebar stubs (or into pipe clips screwed inside the walls) turn the bed into a tunnel in ten minutes — insect mesh against cabbage butterflies and carrot fly in summer, fleece against frost in the shoulder seasons, shade cloth in heat waves. No single accessory extends the harvest more.
• A cold-frame lid on a low bed — an old window hinged to the rim — gives you salads weeks earlier and later, effectively a season-stretching machine built from salvage.
• Vertical add-ons: a trellis panel screwed to the north wall of the bed carries peas, beans, and cucumbers upward, doubling the bed’s output without touching its footprint.

A Maintenance Year (It Is Short)

• Spring: the 3–5 cm compost top-up, a wiggle test on the corner posts, and screws snugged where winter loosened them.
• Summer: water deeply, mulch, and keep soil raked back from constant contact with the top rim — the number-one rot accelerator.
• Autumn: clear spent crops, sow a green manure or blanket the surface with leaves; an empty, bare bed loses soil life and structure to winter rain.
• Every few years: swap any single failing board — three screws out, three screws in — rather than waiting for a wall to slump. A bed maintained this way dies of boredom, not decay.

Five Mistakes That Shorten a Bed’s Life

1. Building too wide and stepping in “just this once” weekly.
2. Plastic-lining the bottom — creating a bathtub in the name of preservation.
3. Skipping the diagonal check, then noticing the rhombus every day for six years.
4. Filling with cheap “topsoil” of mystery origin — weed seeds and worse move in permanently; spend on the top layer.
5. Setting it in the shade because that corner was convenient. The bed is furniture; the sun is the tenant that pays rent.

The Bottom Line

Keep it 120 cm or narrower, 30 cm is plenty tall, choose wood you can name, square it before you fill it, floor it with mesh not plastic, and fill it in layers with the money reserved for the top twenty centimetres. The whole build fits between breakfast and dinner with a lunch break included — and next spring, while the neighbors wrestle their claggy April ground, your soil will be warm, loose, and a fortnight ahead.